The present invention relates to a signal recovery system and more particularly to a symbol synchronization (sync) recovery system for a vestigial sideband (VSB) digital signal.
The recently adopted advanced digital television signal standards are directed to a multilevel signal having two frames of data segments, each frame consisting of 313 segments as shown in FIG. 1. The first segment of each frame includes a two level frame sync signal and each segment has 832 multilevel symbols, wherein the first four symbols of each segment defines a two level segment sync pattern. A small pilot signal is added to aid in carrier recovery in the receiver. The receiver preferably includes a frequency and phase locked loop (FPLL) for recovering the transmitted signal. The data in the transmitted signal is subjected to precoding, interleaving and forward error correcting to provide noise protection and to assist in the rejection of cochannel NTSC signals.
An important requirement of a receiver is the ability to rapidly and accurately achieve symbol acquisition under field operational conditions. The nominal symbol frequency is 10.76 megasymbols per second and ideally, the receiver should acquire symbol frequency lock over a range exceeding +/xe2x88x9270 parts per million (ppm) in under 200 milliseconds.
The related sync signal recovery system has some difficulty achieving the desired symbol acquisition. For example, accurate symbol acquisition is hampered by unacceptable signal-to-noise levels. Moreover, during the transmission of the VSB signal, the original signal sync symbol pattern acquires static such as ghost signals. The ghost signals distort the original sync symbol pattern and prevent an accurate detection of the sync location. Consequently, ghost signals can detrimentally delay the symbol acquisition.
An object of the present invention is to solve at least the problems and disadvantages of the related art.
A further object of the present invention is to rapidly acquire signal synchronization.
Another object of the present invention is to improve the capacity for signal synchronization.
Another object of the present invention is to accurately recover the original sync signal.
Another object of the present invention is to prevent unnecessary delay caused by noise signals.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.